A component of a semiconductor device includes a conduction path. The conduction path is used for, e.g., connecting a semiconductor switching element and a control circuit mounted on an air conditioner together, or connecting a plurality of batteries or capacitors mounted on an electric car together, etc.
As shown in FIGS. 6(a)-6(d), a conduction path generally includes a first conduction path forming plate 51 having a first connection portion, and a second conduction path forming plate 52 having a second connection portion overlapping with the first connection portion of the first conduction path forming plate 51. For example, the first connection portion of the first conduction path forming plate 51 includes a protruding portion 51a which is formed to be incompletely cut to protrude toward the overlapping surface. In contrast, the second connection portion of the second conduction path forming plate 52 includes a through hole 52a which is capable of fitting the protruding portion 51a of the first conduction path forming plate 51 thereinto.
In order to electrically connect the first conduction path forming plate 51 and the second conduction path forming plate 52 together, first, as shown in FIG. 6(a) and FIG. 6(b), the protruding portion 51a of the first conduction path forming plate 51 is inserted into the through hole 52a of the second conduction path forming plate 52, thereby exposing an upper surface of the protruding portion 51a from the through hole 52a. 
Subsequently, as shown in FIG. 6(c), the center of the protruding portion 51a of the first conduction path forming plate 51 exposed from the through hole 52a of the second conduction path forming plate 52 is hammered with a punch 53.
With this process, as shown in FIG. 6(d), an upper part of the protruding portion 51a is pressed and expanded toward a periphery of the through hole 52a of the second conduction path forming plate 52, thereby forming a rivet 51b. 
In this way, a side surface of the protruding portion 51a of the first conduction path forming plate 51 is pressure-welded to a wall surface of the through hole 52a of the second conduction path forming plate 52.
However, such a conventional conduction path has a problem where a pressure welding portion between the side surface of the protruding portion 51a and the wall surface of the through hole 52a has a large electrical resistance, and heat is generated in the pressure welding portion by a current.
Specifically, in the conventional conduction path, the side surface of the protruding portion of the first conduction path forming plate is pressed and expanded toward the wall surface of the through hole of the second conduction path forming plate, whereby the side surface of the protruding portion is pressure-welded to the side wall of the through hole. However, on the first conduction path forming plate 51 and the second conduction path forming plate 52, a metal oxide film is formed in the side surface of the protruding portion 51a and the wall surface of the through hole 52a while the plates are stored in the air before assembly. Therefore, simply pressure-welding the conduction path forming plates 51 and 52 leads to connecting the conduction path forming plates 51 and 52 together with the metal oxide film interposed therebetween, and the electric resistance increases, resulting in generation of excessive heat.
Patent Document 1 discloses, as a countermeasure of metal oxide films in interconnections, and the like, of a semiconductor device, deforming a bonding portion between an electrode and an interconnection in a power semiconductor chip to expose a newly formed surface, thereby improving the strength of the bonding portion.
FIG. 7 illustrates a method of manufacturing the semiconductor device disclosed in Patent Document 1. As shown in FIG. 7, an electrode 102A of a semiconductor chip 102 prior to pressure welding has an uneven surface 102AS. In contrast, an interconnection 103 has a connection portion 103A which is pressure-welded to the electrode 102A. A surface 103AS is flat before the pressure welding is performed. A load is applied by an ultrasonic head, thereby performing the pressure welding of the electrode 102 and the connection portion 103A of the interconnection. At the time of the pressure welding, in each of the electrode 102A and the connection portion 103A, a newly formed surface which is not oxidized is exposed. As a result, a bond strength between the electrode 102A and the connection portion 103A can be improved.
Patent Document 2, which belongs to another technical field, discloses a method of pressure-welding two of clean, newly formed surfaces in order to achieve cold pressure welding.
FIGS. 8(a) and 8(b) illustrate a cross sectional structure of a main part of a conventional method of cold pressure welding disclosed in Patent Document 2.
First, as shown in FIG. 8(a), plate bodies 202a and 202b each having plating layers 208a and 208b on both surfaces thereof overlap each other, and cold pressure welding is performed using a cold pressure welding device. The plate bodies 202a are 202b are made of copper (Cu), and the plating layers 208a and 208b are made of nickel (Ni). Together with the progress of the cold pressure welding, wedge-shaped dice 206a and 206b respectively enter plate bodies 202a and 202b while plastically deforming the plate bodies 202a and 202b toward an arrow A direction and an arrow B direction, respectively. At this time, together with the progress of the cold pressure welding, each of the plating layers 208a and 208b is divided at a pressure welding part 205, and moves toward an arrow C direction and an arrow D direction.
Next, as shown in FIG. 8(b), the plating layers 208a and 208b further move toward the arrow C direction and the arrow D direction, respectively, together with the plastic flow of the plate bodies 202a and 202b by the cold pressure welding. That is because the plating layers 208a and 208b cannot follow the plastic flow of the plate bodies 202a and 202b, respectively, by the cold pressure welding, and the plating layers 208a and 208b reach a breaking point before completion of the pressure welding. As a result, after the plating layer 208a and 208b are divided and are moved, two of clean, newly formed surfaces including no oxide film in each of the plate bodies 202a and 202b are exposed, and the exposed, newly formed surfaces are joined by the cold pressure welding.